Study On The Effects To PHA Synthesis By Activated Sludge Microorganisms

Polyhydroxyalkanoates (PHAs) are accumulated as storage by various microorganisms under growth-limited condition. Its thermoplasticity is similar as oil-derived plastics, and biodegradable property makes it as a good substitute for conventional polymers. Nowadays PHA has been industrially produced by pure cultures. While high substrate costs and aseptic equipment required by pure culture increased the production price to 4-9 times of oil-derived plastics, which stocks wider use of PHA. Researches show that the microorganisms from conventional active sludge used to treat waste water could synthesis PHA. Activated sludge microorganisms use cheap substrate from various sources and don't require sterilized equipment, which remarkably decreases the PHA production price. Culturing activated sludge microorganisms to produce PHA has aroused more and more people notice and becomes research hotspots.This research focuses on the enrichment and acclimation of microorganisms synthesis PHA stage (Stage 2) and PHA accumulation stage (Stage 3) of 3-step process of PHA production. At Stage 2, it compares two different enrichment and acclimation strategies at first,and then studies the impacts of different carbon substrate composition under the better strategy. At Stage 3, two nitrogen and phosphorus supply strategy was employed to encourage PHA accumulation in sludge. The effects are compared which helped to choose a better one used for the study of impacts from different carbon substrate composition then. Microbial community structure is also investigated through 16S rDNA library and terminal restriction fragment length polymorphism (T-RFLP).The results show that: At activated sludge acclimation scenario, two-step acclimation was aroused based on one-step acclimation which is confirmed more suitable for enriching high PHA accumulating ability organisms. Two-step acclimation performed acetate acid utilization rate 210% quicker, biomass concentration 125% more,and PHA storage accomplished in shorter time than the one in one-step. Different carbon substrate composition leads different acclimate result: PHA storage rate is 0.48g PHA/g organic carbon when substrate contains 20mM/L sodium acetate and 10mM/L sodium propionate. At PHA production scenario, Nitrogen/phosphorus supply gradually reduce strategy is more efficient than directly reduce strategy to improve PHA accumulation. Using directly reduce strategy the PHA content reaches 12.02% of dry sludge. While using gradually reduce strategy PHA content increased to 38.00% of dry sludge with 10mM/L sodium acetate and 20mM/L sodium propionate as carbon source. With sodium acetate as the only carbon source HV mole content takes up 45.51% of polymer, which is much higher than former reports. HV content raises followed with sodium propionate concentration increases in substrate. The highest HV content, 81.50% of polymer, obtained when sodium propionate is the only carbon source. Microbial structure analysis shows that, Alpha proteobacterium,Meganema perideroedes,Paracoccus sp. and Rhodobacteraceae bacterium are the dominant spices in PHA accumulated sludge, which are all belong toα-proteobacteria. With the increase of sodium acetate concentration the abundance of Alpha proteobacterium,Meganema perideroedes , Paracoccus sp. increase, but abundance of Rhodobacteraceae bacterium goes down. The lower richness of microbial community is, the higher PHA content could be harvested. The similar carbon composition leads to similar microbial community structure.